The work was developed for a neighborhood in the city of Luanda, on the basis of a digital elevation model (DEM) of high spatial resolution, with data from different sources, for simulating hydrologic and hydraulic processes, as part of a strategy for designing storm sewer networks applying mathematical modeling. Fourier analysis tools and filtering were used to reduce the fluctuations of local character from the DEM. In the filtering process, it was ensured that the chosen filter completely eliminated all local fluctuations of high-frequency components and leaves only the desired low-frequency trend components.